This chapter begins with a discussion of the attributes of living organisms. These include growth, reproduction, response to stimuli, metabolism, movement, complexity of organization, and adaptation to the environment. Then it examines the chemical and physical bases of life. A brief look at the elements and their atoms is followed by a discussion of compounds, molecules, valence, bonds, ions, acids, bases, and salts. Forms of energy and the chemical components of cells are examined next. The chapter concludes with an introduction to macromolecules: carbohydrates, lipids, proteins, and nucleic acids.
Some Learning Goals
1. Learn the attributes of living organisms.
2. Define matter; describe its basic state.
3. Understand the nature of compounds and describe acids, bases, and salts.
4. Know the various forms of energy.
5. Learn the elements found in cells.
6. Understand the nature of carbohydrates, lipids, and proteins.
ave you ever dropped a pellet of dry ice (frozen
H carbon dioxide) into a pan of water and watched what happens? The solid pellet darts randomly about the surface, looking like a highly energetic bug waterskiing, as the warmer water rapidly converts it to a gas. Does all that motion make the dry ice alive? Hardly; yet one of the attributes of living things is the capacity to move. But if living things move, what about plants? If a tree remains fixed in one place and doesn't crawl down the sidewalk, does that mean it isn't alive? Again the answer is no, but these questions do serve to point out some of the difficulties encountered in defining life. In fact, some argue that there is no such thing as life—only living organisms—and that life is a concept based on the collective attributes of living organisms.
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